This invention relates to a method and apparatus for fusing together thermoplastic synthetic resin molded articles, and more particularly a method and apparatus for fusing together thermoplastic synthetic resin molded articles wherein the molded articles are urged against a heating plate to melt their surfaces and the molten surfaces are fused together.
It has been known to obtain a desired product, for example a pallet, by fusing together a plurality of synthetic resin molded articles formed by an injection molding machine, an extrusion molding machine or the like, and fusing apparatus having various constructions have been used depending upon the type of the product.
The fusing apparatus of this type usually comprises a holding mechanism for holding articles to be fused together in an opposed relation, a reciprocatable heating plate for melting the surfaces of the articles to be fused together and a pair of press boards for abutting under pressure the molten surfaces of the molded articles.
When fusing together thermoplastic synthetic resin molded articles by using such apparatus, it is necessary to uniformly heat and melt the surfaces of the articles. Accordingly, it has been the practice to urge the surfaces of the molded articles to be fused together against a heating plate heated to a uniform temperature, the engaged state is maintained for a suitable interval to form uniformly melted layers of the resin and then the molded articles are separated away from the heating plate.
Since the surfaces of the molded articles in contact with the heating plate are in a molten state when the molding articles are separated away from the heating plate, a portion of the molten resin often remains on the surface of the heating plate.
Upon occurrence of such state, the molten surfaces of the molded articles to be fused together become irregular or a portion of the molten resin layers formed on the surfaces of the molded articles drops off with the result that the fused portions of the resulting product become nonuniform thus decreasing the mechanical strength thereof.
The thermoplastic synthetic resin adhered to the surface of the heating plate tends to degrade. For this reason, the degraded resin accumulated in the preceding operations would adhere to the surfaces of the molded articles to be melted in the later operation. This also causes decrease in the mechanical strength of the product.
To overcome these defects, in the fusing apparatus of the type described above Teflon resin or the like was coated on the surface of the heating plate for preventing the molten resin from adhering thereto.
However, since the durability of the teflon resin or the like is not sufficiently high, it is necessary to apply again the coating in a short time, thus not only increasing the manufacturing and reparing costs of the heating plate but also making it difficult to obtain satisfactory heating plate.